The instant invention relates to an inductive angle-of-rotation sensor in which a rotatable magnetically conductive element is positioned within a coil body.
An angle-of-rotation sensor of this type is known from DE 43 35 594 A1 (U.S. Pat. No. 5,455,508).
This known angle-of-rotation sensor operates on the principle that a variation takes place in the ratio of the inductances of two windings which are wound on a coil body as a result of rotation of a magnetic conductive element mounted rotatably within the coil body. An arrangement of this type can thus be compared to a transformer with a variable degree of coupling.
In order to produce a signal characterizing the angle of rotation, a.c. voltage is fed into the first coil winding in this known angle-of-rotation sensor. This a.c. voltage induces a certain output voltage in the second coil winding which is a function of the inductance ratio of the two coil windings, and also a function of the angular position of the magnetic conductive element. The ratio between the amplitude of this output voltage and the amplitude of the input voltage fed into the first coil winding therefore represents a measure of the sensed angle of rotation of the magnetic conductive element.
The disadvantage of this principle of operation is that in order to operate the angle-of-rotation sensor, a high-frequency a.c. voltage signal is required, the form of which is sinusoidal. However, sensors of this type are normally used in combination with electronic systems carrying out the evaluation of the sensor signals. Such, electronic systems are at this time almost always based on digital technology. Since these systems usually are also equipped with a microprocessor for the control of other functions in addition to the evaluation of signals from a sensor, it is desirable to operate sensors of such systems with signals that are commonly used in digital electronic systems having microprocessors. A sinusoidal a.c. voltage is not such a signal.
Operation of the known angle-of-rotation sensor with a rectangular a.c. voltage signal normally used in digital technology would have the disadvantage that the harmonics accompanying such a signal may cause undesirable and sometimes unexpected resonance effects which could result in a deterioration of the electronic system with respect to its electromagnetic compatibility with other electronic systems.
Another disadvantage of the operating principle of the known angle-of-rotation sensor is the fact that the output signal carried in the second coil winding is also an a.c. voltage signal. Since it is necessary for the sensing of the angle-of-rotation sensor to measure the amplitude of the output signal, it is necessary in a digital electronic system to transform this output signal by means of a rectifier, and possibly by means of an amplifier as well, into a d.c. voltage signal of suitable magnitude. In this case, the d.c. voltage signal must be of a magnitude which can be processed by an analog/digital converter. Electronic circuit components such as rectifiers, amplifiers and analog/digital converters are expensive components and should therefore be avoided, if possible.
In addition to the above-mentioned disadvantages, the known angle-of-rotation sensor has the additional disadvantage that because two coil windings are employed, at least three but usually even four electrical connections are necessary. A suitable plug-in connector for the connection of such an angle-of-rotation sensor requires therefore at least three and possibly even four electrical contacts. For many applications, however, it is advantageous to use sensors with as few electrical connections as possible.
It is therefore the object of the present invention to provide an inductive angle-of-rotation sensor in a simplified form, with as few electrical connections as possible, which could furthermore be used in a digital electronic system, preferably, in a digital electronic system which includes a microprocessor, and without using analog circuit means.
Analog circuit means are understood in this context to be electronic circuit means suited exclusively or especially for the processing of analog signals, and includes, e.g., rectifier, analog/digital converter, analog amplifier, sinoid generator, etc.